The present invention is directed to hot melt or phase change inks. More specifically, the present invention is directed to phase change inks particularly suitable for use in phase change ink jet printers. One embodiment of the present invention is directed to a phase change ink composition comprising (a) a colorant, (b) a phase change ink carrier, and (c) an antioxidant or UV stabilizer molecule of the formula 
wherein R1, R2, R3, R4, R5, R6, R7, R8, and R9 each, independently of the others, is (i) a hydrogen atom, (ii) a hydroxy group, (iii) an amino group, (iv) an alkyl group, (v) an aryl group, (vi) an arylalkyl group, (vii) an alkylaryl group, (viii) an alkoxy group, (ix) an aryloxy group, (x) an arylalkyloxy group, (xi) an alkylaryloxy group, (xii) a halogen atom, (xiii) a cyano group, (xiv) an aldehyde group, (xv) a ketone group, (xvi) an ester group, (xvii) an amide group, (xviii) a sulfide group, (xix) a sulfoxide group, (xx) a nitrile group, (xxi) a sulfone group, (xxii) an acyl group, or (xxiii) a carboxylic acid group, provided that at least one of R1, R2, R3, R4, R5, R6, R7, R8, and R9 is an alkyl group having at least about 8 carbon atoms, an alkoxy group having at least about 8 carbon atoms, an aryl group having at least about 6 carbon atoms, an aryloxy group having at least about 6 carbon atoms, an arylalkyl group having at least about 7 carbon atoms, an arylalkyloxy group having at least about 7 carbon atoms, an alkylaryl group having at least about 7 carbon atoms, or an alkylaryloxy group having at least about 7 carbon atoms.
In general, phase change inks (sometimes referred to as xe2x80x9chot melt inksxe2x80x9d) are in the solid phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops. Phase change inks have also been used in other printing technologies, such as gravure printing, as disclosed in, for example, U.S. Pat. No. 5,496,879 and German Patent Publications DE 4205636AL and DE 4205713AL, the disclosures of each of which are totally incorporated herein by reference.
Phase change inks for color printing typically comprise a phase change ink carrier composition which is combined with a phase change ink compatible colorant. In a specific embodiment, a series of colored phase change inks can be formed by combining ink carrier compositions with compatible subtractive primary colorants. The subtractive primary colored phase change inks can comprise four component dyes, namely, cyan, magenta, yellow and black, although the inks are not limited to these four colors. These subtractive primary colored inks can be formed by using a single dye or a mixture of dyes. For example, magenta can be obtained by using a mixture of Solvent Red Dyes or a composite black can be obtained by mixing several dyes. U.S. Pat. No. 4,889,560, U.S. Pat. No. 4,889,761, and U.S. Pat. No. 5,372,852, the disclosures of each of which are totally incorporated herein by reference, teach that the subtractive primary colorants employed can comprise dyes from the classes of Color Index (C.I.) Solvent Dyes, Disperse Dyes, modified Acid and Direct Dyes, and Basic Dyes. The colorants can also include pigments, as disclosed in, for example, U.S. Pat. No. 5,221,335, the disclosure of which is totally incorporated herein by reference. U.S. Pat. No. 5,621,022, the disclosure of which is totally incorporated herein by reference, discloses the use of a specific class of polymeric dyes in phase change ink compositions.
Phase change inks have also been used for applications such as postal marking, industrial marking, and labelling.
Phase change inks are desirable for ink jet printers because they remain in a solid phase at room temperature during shipping, long term storage, and the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with liquid ink jet inks are largely eliminated, thereby improving the reliability of the ink jet printing. Further, in phase change ink jet printers wherein the ink droplets are applied directly onto the final recording substrate (for example, paper, transparency material, and the like), the droplets solidify immediately upon contact with the substrate, so that migration of ink along the printing medium is prevented and dot quality is improved.
Compositions suitable for use as phase change ink carrier compositions are known. Some representative examples of references disclosing such materials include U.S. Pat. No. 3,653,932, U.S. Pat. No. 4,390,369, U.S. Pat. No. 4,484,948, U.S. Pat. No. 4,684,956, U.S. Pat. No. 4,851,045, U.S. Pat. No. 4,889,560, U.S. Pat. No. 5,006,170, U.S. Pat. No. 5,151,120, U.S. Pat. No. 5,372,852, U.S. Pat. No. 5,496,879, European Patent Publication 0187352, European Patent Publication 0206286, German Patent Publication DE 4205636AL, German Patent Publication DE 4205713AL, and PCT Patent Application WO 94/04619, the disclosures of each of which are totally incorporated herein by reference. Suitable carrier materials can include paraffins, microcrystalline waxes, polyethylene waxes, ester waxes, fatty acids and other waxy materials, fatty amide containing materials, sulfonamide materials, resinous materials made from different natural sources (tall oil rosins and rosin esters, for example), and many synthetic resins, oligomers, polymers, and copolymers.
Japanese Patent Publication JP 09255696-A2, the disclosure of which is totally incorporated herein by reference, discloses a benzophenone derivative having an oxyalkylene group thereon which exhibits UV light-absorbing effects and water solubility, said derivative being of the formula 
wherein R1 and R2 are each hydrogen atoms, hydroxyl groups, or alkoxy groups with 1 to 4 carbon atoms, R3, R4, R5, and R6 are each hydrogen or an alkyl group with 1 to 2 carbon atoms, wherein one or more of R3 to R6 is alkyl, A is a saccharide group not having a protecting group, and n is 1 or 2. The derivative is prepared by, for example, reacting 2,4-dihydroxybenzophenone with propylene oxide in the presence of sodium bicarbonate in ion-exchanged water at reflux temperature. Also disclosed are preparations containing the derivative and used for external application to skin.
U.S. Pat. No. 4,256,493 (Yokoyama et al.), the disclosure of which is totally incorporated herein by reference, discloses a jet ink composition which comprises an aqueous jet ink containing a water-soluble dye, a wetting agent and water as main components and, incorporated therein, a water-soluble ultraviolet absorbing agent as well as a metal salt, when necessary.
U.S. Pat. No. 5,643,356 (Nohr et al.). the disclosure of which is totally incorporated herein by reference, discloses an improved ink suitable for ink jet printing comprising a mixture of a colorant, an arylketoolkene stabilizing compound or a photoreactor, and a liquid vehicle, wherein the colorant is light-stable. When the photoreactor is combined with a wavelength-selective sensitizer to form a radiation transorber, the colorant is mutable upon exposure of the radiation transorber to specific, narrow bandwidth radiation. The colored composition may also contain a molecular includant having a chemical structure which defines at least one cavity wherein each of the colorant and photoreactor or radiation transorber is associated with the molecular includant. The invention also includes ink jet print cartridges containing the improved ink, ink jet printers containing the improved ink and methods of printing using the improved ink.
U.S. Pat. No. 5,855,655 (Nohr et al.), the disclosure of which is totally incorporated herein by reference, discloses an ink set of inks which have substantially identical light fastness properties. The ink set includes ink compositions containing a colorant and at least one colorant stabilizer. The colorant stabilizer imparts light-stability to the colorant so that the colorant does not fade when exposed to electromagnetic radiation such as sunlight or artificial light. The ink set provides a range of colored inks having similar light-stability.
PCT Patent Publication WO 97/20000 (Nohr et al.), the disclosure of which is totally incorporated herein by reference, discloses colorant stabilizers and a colorant composition which includes a colorant and a colorant stabilizer. The colorant stabilizer imports light-stability to the colorant so that the colorant does not fade when exposed to electromagnetic radiation such as sunlight or artificial light.
While known compositions and processes are suitable for their intended purposes, a need remains for improved phase change ink compositions. In addition, a need remains for phase change ink compositions with improved lightfastness. Further, a need remains for phase change ink compositions suitable for use in the production of digital photographs. Additionally, a need remains for phase change ink compositions suitable for generating prints with good archival qualities. There is also a need for phase change ink compositions with the above advantages which can be, if desired, of relatively simple composition. In addition, there is a need for phase change inks containing antioxidants and/or UV stabilizers that are soluble within the ink carrier. Further, there is a need for phase change inks with the above advantages that exhibit desirable jetting characteristics.
The present invention is directed to a phase change ink composition comprising (a) a colorant, (b) a phase change ink carrier, and (c) an antioxidant or UV stabilizer molecule of the formula 
wherein R1, R2, R3, R4, R5, R6, R7, R8, and R9 each, independently of the others, is (i) a hydrogen atom, (ii) a hydroxy group, (iii) an amino group, (iv) an alkyl group, (v) an aryl group, (vi) an arylalkyl group, (vii) an alkylaryl group, (viii) an alkoxy group, (ix) an aryloxy group, (x) an arylalkyloxy group, (xi) an alkylaryloxy group, (xii) a halogen atom, (xiii) a cyano group, (xiv) an aldehyde group, (xv) a ketone group, (xvi) an ester group, (xvii) an amide group, (xviii) a sulfide group, (xix) a sulfoxide group, (xx) a nitrile group, (xxi) a sulfone group, (xxii) an acyl group, or (xxiii) a carboxylic acid group, provided that at least one of R1, R2, R3, R4, R5, R6, R7, R8, and R9 is an alkyl group having at least about 8 carbon atoms, an alkoxy group having at least about 8 carbon atoms, an aryl group having at least about 6 carbon atoms, an aryloxy group having at least about 6 carbon atoms, an arylalkyl group having at least about 7 carbon atoms, an arylalkyloxy group having at least about 7 carbon atoms, an alkylaryl group having at least about 7 carbon atoms, or an alkylaryloxy group having at least about 7 carbon atoms.